Stator core, a stator and a motor

ABSTRACT

A stator core, a stator and a motor are provided. The stator core may includes a head that extends in a circumferential direction; a tooth that extends inward from the head; a first protruding portion that extends outward from an outer circumferential surface of the head; and a second protruding portion that protrudes from an outer circumferential surface of the first protruding portion.

CROSS-REFERENCE TO RELATED APPLICATION

The application claims priority under 35 U.S.C. § 119 to KoreanApplication No. 10-2015-0049105, filed in Korea on Apr. 7, 2015, whoseentire disclosure is incorporated herein by reference.

BACKGROUND

1. Field

Embodiments relate to a stator core, a stator and a motor.

2. Background

An EPS (Electronic Power Steering) system may be used in order to securesteering stability of a vehicle. In the EPS system, an ECU (ElectronicControl Unit) may drive a motor depending on driving conditions detectedby sensors, such as, e.g., a speed sensor, a torque angle sensor, and atorque sensor. The EPS system may secure turning stability and rapidstability restoring force so that a driver may drive a vehicle safely.

In the EPS system, a motor assists in a torque of a steering wheel sothat the driver may operate the steering wheel with less physical power.The motor may be a BLDC (Brushless Direct Current) motor. Principalcomponents of the BLDC motor include a stator and a rotor. A coil iswound on the stator, and a magnet is coupled to the rotor so that therotor may rotate via a mutual electromagnetic interaction. In the EPSmotor, performance of the motor depends on how a friction torque, or amechanical or frictional component generated during rotation of themotor, may be reduced.

BRIEF DESCRIPTION OF DRAWINGS

The embodiments will be described in detail with reference to thefollowing drawings in which like reference numerals refer to likeelements wherein:

FIG. 1 is a plan view illustrating a stator core according to anembodiment;

FIG. 2 is a conceptual view of a structure of FIG. 1;

FIG. 3 is a plan view illustrating a stator according to an embodiment;

FIG. 4 is a plan view illustrating a partial structure of a motoraccording to an embodiment;

FIG. 5 is an enlarged perspective view illustrating a portion of a motoraccording to an embodiment;

FIG. 6 is a graph illustrating a result of an experiment for reducingfriction according to an embodiment; and

FIG. 7 is a sectional view illustrating a motor according to anembodiment.

DETAILED DESCRIPTION

Referring to FIGS. 1 to 3, a stator 100 according to an embodiment mayinclude a plurality of stator cores 110 having a tooth 112 protrudedfrom a head part 111. The stator 100 may be formed by coupling theplurality of stator cores 110. The plurality of stator cores 110 may beadjacent to one another and may be coupled such that an outercircumferential surface of the head parts 111 form a circular shape. Atleast two stepped areas a2, a3 may be provided at the head part 111 ofthe stator core 110, and a straight distance of the respective steppedareas a2, a3, from an inner end of the tooth 112 to an outercircumferential surface of the head part 111, is different from eachother.

As illustrated in FIG. 1, the stepped area a2, a3 may be defined as anarea each having a different straight distance measured from an innerend (A) to an outer circumferential surface of the head part 111including a curved surface having a predetermined curvature. Each of thestepped areas a2, a3 may form an area of a structure having apredetermined curvature surface. The area may contact a surface of themotor housing and may be located higher than another area of the atleast two stepped areas. The other area of the at least two steppedareas, which may be lower, may form a separated area spaced apart fromthe motor housing so as to reduce a frictional area. Two of the steppedareas may be provided at the head part of the stator core. However, theembodiment is not limited thereto, and a greater number of stepped areasmay be implemented at the stator core.

As illustrated in FIG.1, the stepped area a2, a3 may include a firststepped area a2 having a bidirectional first curvature surface at acenter line (X), and a second stepped area a3 extended from a distal endof the first stepped area a2 and having a second curvature surface ofwhich the straight distance may be longer than that of the first steppedarea a2. Although a height of the second stepped area a3 as shown in thefigures is higher than that of the first stepped area a2, conversely,the first stepped area a2 may have a height (straight distance) higherthan that of the second stepped area a3.

A stepped groove a1 formed in a direction towards the tooth 112 may beadditionally provided at a position where the center line (X) encountersthe outer circumferential surface of the head part 111. The steppedgroove a1 may have a depth deeper than that of the first stepped areaa2. Although not illustrated in the figures, a friction reducing patternincluding a plurality of inwardly recessed grooves having a structuresimilar to that of the stepped groove a1 may be provided at at least oneof an outer circumferential surface of the first stepped area a2 and anouter circumferential surface of the second stepped area a3. Thus,frictional index of the surfaces may be further reduced.

As illustrated in FIG. 2, the stator core 110 having a structure asillustrated in FIG. 1 may have a structure where a radius (R2) of avirtual circle is different from a radius (R1) of a virtual circle. Theradius (R2) may be a radius of a virtual circle where the curvaturesurface of the first stepped area a2 extends, and the radius (R1) refersto a radius of a virtual circle where the curvature surface of thesecond stepped area a3 extends.

If a plurality of the stator cores 110 is combined to form the stator100 as illustrated in FIG. 3, an outer circumferential surface of thestator 100 may correspond to the virtual circle having the radius (R1)as illustrated in FIG. 2. For example, the second stepped areas a3 ofadjacently arranged stator cores 110 may all have equal height andcurvature such that height deviation may be eliminated in a combinedstructure of the plurality of the stator cores 110. Thus, friction withan external housing may be reduced.

As illustrated in FIGS. 4 and 5, if a contact area (Y) between thestepped areas a2, a3 and an inner surface of a housing 500 of a motor isenlarged, a separated portion between the first stepped area a2 and aninner surface of the housing 500 of the motor may be shown to beprovided at the head part 111 of the stator core 110. The separatedportion may reduce a contact area between the stator 100 and the housing500 of the motor such that friction may be reduced on the whole.

TABLE 1 shows results of friction torque of an embodiment having thestepped areas a2, a3 and a comparative embodiment, under a conditionthat a stator core of a same standard is provided. In this embodiment,the first stepped area a2 formed a 5 mm section in left and rightdirections on the basis of the center line (X), and 30 rpm of drivingpower was applied in the experiment.

TABLE 1 Friction Torque (30 rpm) Comparative Embodiment ExemplaryEmbodiment CW CCW CW CCW #Sample 1 16.88 16.59 12.97 12.69 #Sample 217.57 17.13 13.66 13.09 #Sample 3 16.41 16.25 13.27 12.58 AVERAGE 16.9516.66 13.30 12.79

As shown in TABLE 1, friction torque may be reduced by approximately amaximum of 25% when a stator core includes the stepped areas a2, a3 ascompared to the comparative embodiment. Similar results may also beshown in the graph of FIG. 6, where friction torque is significantlyreduced in an embodiment with a stepped area (Gap) according to thepresent disclosure in comparison with a comparative embodiment.

Hereinafter, an example of an EPS (Electronic Power Steering) motoremploying the stator core 110 according to an embodiment of the presentdisclosure may be described. However, the stator core 110 may be appliedto various types of motors. Referring to FIG. 7, a motor housing 500 anda bracket 30 coupled to the housing 500 may be provided. An uppersurface of the housing 500 may be opened, and a support pipe 11 may beprotruded from a center of a lower surface of the housing 500. A firstbearing 31 may be installed at the support pipe 11, and a second bearing32 may be installed at the bracket 30. A shaft 400 may contact andsupport the first bearing 31 and the second bearing 32. An upper portionof the shaft 400 may be supported by the second bearing 32, and a lowerportion of the shaft 400 may be supported by the first bearing 31.

An upper end of the shaft 400 may be upwardly protruded and penetratethrough the bracket 30, and may be combined with instruments 60connected to a steering shaft. A stator 100 and a rotor 300 may beinstalled inside of the housing 500. The rotor 300 may include a rotorcore 320 coupled to the shaft 400, and a magnet 310 coupled to an outercircumferential surface of the rotor core 320. Although a structurewhere the magnet 310 is coupled to an outer circumferential surface ofthe rotor core 320 is shown in FIG. 7, another structure where themagnet 310 is inserted in the rotor core 320 may also be applied. Thestator 100 may include a stator core 110 arranged between the magnet 310and the housing 110, and a coil 120 wound on the stator core 110.

The stepped areas a2, a3 as previously described in FIGS. 1 to 5 may beapplied to the stator core 110 composing the stator 100. The shaft 400may rotate by interaction between a magnetic field generated from thestator 100 and a magnetic field generated from the rotor 300. A sensingplate 40 may be coupled to the shaft 400 to rotate with the shaft 400,and a sensing magnet 50 may be installed at the sensing plate 40. Acircuit board 10 may be installed at the bracket 30, and a sensingelement or sensor 20 facing the sensing magnet 50 may be installed atthe circuit board 10. The sensing element 20 may sense an extent ofrotation of the sensing magnet 50 so as to sense rotation of the sensingplate 40 coupled with the sensing magnet 50 and the shaft 400.

According to embodiments disclosed herein, the stator core 110 mayinclude a head part 111, a tooth 112, a first protruding part or portion114, and a second protruding part or portion 115. The stator core 110may include a head part 111 extended in a circumferential direction. Thestator core 110 may include a tooth 112 inwardly extended from the headpart 111. The stator core 110 may include a first protruding part 114outwardly protruded from an outer circumferential surface 113 of thehead part 111. The stator core 110 may include a second protruding part115 outwardly protruded from an outer circumferential surface of thefirst protruding part 114.

The first protruding part 114 may include a first protrusion 114 a and asecond protrusion 114 b. The first protruding part 114 may include afirst protrusion 114 a provided in a first direction of acircumferential direction from the outer circumferential surface 113 ofthe head part 111; and a second protrusion 114 b provided in a seconddirection opposite to the first direction from the outer circumferentialsurface 113 of the head part 111. The first protrusion 114 a and thesecond protrusion 114 b may be symmetrical around a center of the headpart 111. A length of the first protrusion 114 a in the circumferentialdirection may be longer than a length of the outer circumferentialsurface 113 of the head part 111 in the circumferential direction. Thefirst protruding part 114 may include an inclined part 116 inclinedlyconnecting an outer circumferential surface 113 of the head part 111 andan outer circumferential surface of the first protruding part 114.

The second protruding part 115 may include a third protrusion 115 a anda fourth protrusion 115 b. The second protruding part 115 may include athird protrusion 115 a provided in the first direction from the firstprotrusion 114 a; and a fourth protrusion 115 b provided in the seconddirection from the second protrusion 114 b. The third protrusion 115 aand the fourth protrusion 114 b may be symmetrical around a center ofthe head part 111. A length of the third protrusion 115 a in thecircumferential direction may be longer than a length of the firstprotrusion 114 a in the circumferential direction and shorter than alength of the outer circumferential surface 113 of the head part 111 inthe circumferential direction. A length of the first protruding part 114outwardly protruded from the outer circumferential surface 113 of thehead part 111 may be longer than a length of the second protruding part115 outwardly protruded from the outer circumferential surface of thefirst protruding part 114.

A friction reducing pattern including a plurality of inwardly recessedgrooves may be formed at least one of the outer circumferential surface113 of the head part 111 and the outer circumferential surface of thefirst protruding part 114.

The stator 100 may be formed by a structure where a plurality of thestator cores 110 is arranged in a circumferential direction. Theplurality of the stator cores 110 may be integrally formed. The motoraccording to embodiments disclosed herein may include the stator 100,and the housing 500 internally accommodating the stator 100. An outercircumferential surface of the second protruding part 115 may contactwith an inner circumferential surface of the housing 500.

An external diameter of approximately 5 mm sections at both sides of thestator may be reduced such that an area contacting the housing 500 maybe reduced to form an air gap. For example, a plurality of the statorcores 110 may be indented and assembled with the housing 500, such thateighteen sections contact the housing 500 and remaining sections formair gaps to reduce friction torque. The air gaps between the housing 500and the stator 100 are formed or provided to reduce friction torque.

In order to reduce friction torque of the motor as described above, atleast two stepped areas may be provided, where the stepped areas aredifferent from each other in height. Thus, frictional torque may bereduced by reducing a frictional index when a stator is installed in thehousing.

Embodiments disclosed herein provide a plurality of stator cores, thestator core including a tooth protruded from a head part or head,wherein the plurality of stator cores may be adjacent to one another andcoupled such that an outer circumferential surface of the head part mayform a circular shape, wherein at least two stepped areas may beprovided on the head part. A straight direction, from one end of thetooth to the outer circumferential surface of the head part, of therespective stepped area may be different from each other.

Embodiments disclosed herein also provide a motor, the motor including amotor housing; a stator including the plurality of stator cores, eachincluding a tooth protruded from a head part or head; and a rotorrotatably installed at a center of the stator, and including athrough-hole formed at a center and a magnet module, wherein at leasttwo stepped areas may be provided at the head part of the stator core,where a straight distance of the respective stepped areas, from one endof the tooth to an outer circumferential surface of the head part, maybe different from each other, and wherein any one of the at least twostepped areas may contact an inner circumferential surface of the motorhousing.

The stator core may include a head part extended in a circumferentialdirection; a tooth inwardly extended from the head part; a firstprotruding part or portion outwardly protruded from an outercircumferential surface of the head part; and a second protruding partor portion outwardly protruded from an outer circumferential surface ofthe first protruding part. The first protruding part may include a firstprotrusion provided in a first direction of the circumferentialdirection from the outer circumferential surface of the head part; and asecond protrusion provided in a second direction opposite to the firstdirection from the outer circumferential surface of the head part.

The first protrusion and the second protrusion may be symmetrical aboutor around a center of the head part. A length of the first protrusion inthe circumferential direction may be longer than a length of the outercircumferential surface of the head part in the circumferentialdirection. The first protruding part may include an inclined part orportion inclinedly connecting an outer circumferential surface of thehead part and an outer circumferential surface of the first protrudingpart. The second protruding part may include a third protrusion providedin the first direction from the first protrusion; and a fourthprotrusion provided in the second direction from the second protrusion.

The third protrusion and the fourth protrusion may be symmetrical aboutor around a center of the head part. A length of the third protrusion inthe circumferential direction may be longer than a length of the firstprotrusion in the circumferential direction, and shorter than a lengthof the outer circumferential surface of the head part in thecircumferential direction. A length of the first protruding partoutwardly protruded from the outer circumferential surface of the headpart may be longer than a length of the second protruding part outwardlyprotruded from the outer circumferential surface of the first protrudingpart. A friction reducing pattern including a plurality of inwardlyrecessed grooves may be formed at least one of the outer circumferentialsurface of the head part and the outer circumferential surface of thefirst protruding part.

The stator may include a first stator core and a second stator corecouple to the first stator core in a circumferential direction, whereinthe first stator core includes a head part or head extended in acircumferential direction; a tooth inwardly extended from the head part;a first protruding part or portion outwardly protruded from an outercircumferential surface of the head part; and a second protruding partor portion outwardly protruded from an outer circumferential surface ofthe first protruding part. The first stator core and the second statorcore may be integrally formed.

The motor may include a stator core including a head part or headextended in a circumferential direction, a tooth inwardly extended fromthe head part, a first protruding part or portion outwardly protrudedfrom an outer circumferential surface of the head part, and a secondprotruding part or portion outwardly protruded from an outercircumferential surface of the first protruding part; and a housinginternally accommodating the stator core, wherein an outercircumferential surface of the second protruding part has an innercontact with an inner circumferential surface of the housing.

The terms including ordinal numbers such as “first” or “second” may beused for description of various elements. However, the elements shallnot be limited by such the terms. The terms are used merely todistinguish a particular element from another element.

Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with any embodiment, it is submitted that it is within thepurview of one skilled in the art to effect such feature, structure, orcharacteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. A motor, comprising: a housing; a stator disposedwithin the housing; a rotor disposed inside the stator; and a shaftcoupled with the rotor, wherein the stator has a plurality of dividedstator cores, at least one of the plurality of divided stator coresincluding a head in contact with the housing and a tooth protruding fromthe head toward a center of the stator, wherein the head includes anouter circumferential surface facing the housing, wherein at least twostepped areas are provided in the outer circumferential surface, whereinthe at least two stepped areas includes a first outer circumferentialsurface and a second outer circumferential surface, wherein a straightdistance from an inner end of the tooth to the second outercircumferential surface is larger than a straight distance from theinner end of the tooth to the first outer circumferential surface,wherein the second outer circumferential surface having a curvaturesurface with a predetermined curvature, wherein the first outercircumferential surface is not in contact with the housing and thecurvature surface of the second outer circumferential surface contactsan inner curved surface of the housing, and wherein a first recessedgroove is provided from the first outer circumferential surface and asecond recessed groove is provided from the curvature surface of thesecond outer circumferential surface.
 2. The motor of claim 1, whereinthe first recessed groove comprises inwardly recessed grooves.
 3. Themotor of claim 1, wherein a length of the first outer circumferentialsurface in a circumferential direction is shorter than a length of thesecond outer circumferential surface from a first end to a second end inthe circumferential direction.
 4. The motor of claim 1, wherein a lengthof the first outer circumferential surface in the circumferentialdirection is longer than a length of the second outer circumferentialsurface in the circumferential direction.
 5. The motor of claim 1,wherein each of the plurality of divided stator cores is symmetricallyformed with respect to a center line.
 6. The motor of claim 5, whereinthe first recessed groove on the first outer circumferential surface isa groove provided at a position where the center line encounters thefirst outer circumferential surface and formed in a direction to whichthe tooth is protruded.